Evaluation Of Temperature Difference Control Scheme For Reactive Distillation Columns

In the actual production process of petrochemical, the important component from the raw material, intermediate or coarse product is often separated, and the distillation is the most commonly used method. It is known that if the component in the mixture is different, the corresponding volatility is also different. Based on the principle, the distillation process is to make the heavy component in the vapor phase and the light component in the liquid phase transfer from each other, and then the goal of separating the components is realized. Reactive distillation column (RDC) is a plant that combining reactive operation and separated operation, it has huge economic advantages and is worth to study because of its abilities of reducing investment and improving thermodynamic efficiency. Reaction distillation process is a multivariable process including multiple inputs and multiple outputs, and it has complex internal mechanism, lagging dynamic response and strong correlation relationship between variables. The process control requirement in technological process is relatively high, so a reasonable control scheme for RDC is needed.The control effect of temperature control (TC) scheme in the RDC is not well when operating pressure is changed. In order to solve problem, temperature difference control (TDC) scheme is proposed in this paper. For the RDC with double reactants and two products that are from the top and bottom respectively, three temperature control loops are included in TDC scheme. Two of the control loops are designed in the location that close to products respectively, thus purity of the products of double sides are ensured. In order to control the two reactants feeding ratio determined by the chemical reaction coefficient of measurement, the third loop is located in the middle position of the two kinds of feed. In addition, for the RDC system with the most unfavorable relative volatility, the two products are out of the middle location, so the TDC scheme includes two temperature difference control loops, which are used to control the reboiler heat duty and one of the feed flow rates respectively. Here the actual systems named methyl acetate reaction rectification and isopropyl palmitate reaction distillation are taken as examples to verify the control effect of the TDC scheme. By comparing with the TC scheme, the simulation results show that the TDC system can avoid the disturbance of larger changes in operating pressure and the TC system can't reach a steady-state. In addition, whatever the kind of feed disturbance, the control effect of TDC scheme is always better than TC scheme. Thus the results verify the feasibility of TDC scheme when it is applied to the RDC. And the TDC scheme should be regarded as a novel and effective control scheme used in the reaction distillation process in the future.